<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <script src="script/jquery-1.7.2.js"></script>
  <script>
    $(function () {
      $("#btn0").click(
        function () {
          $("div").html("<h1>我是div中的标题</h1>");
          var a;
          // "undefined" == typeof a
          if (a == undefined){
            alert("aaundefined")
          }

        }
      )
      $("#btn1").click(
        function () {
          $("h1").text("我变化了")
          $("#btn1").text("改变了")
        }
      )
      $("#btn2").click(
        function () {
          alert($("input").val())
          $("input").val("张保国最帅")
        }
      )
    })

  </script>
</head>
<body>
<button id="btn0">html测试</button>
<button id="btn1">text测试</button>
<button id="btn2">表单项目测试</button>

<div>我是div标签
  <span>我是span标签</span>
  <input type="text" value="默认文本">
</div>
</body>
</html>
